Elastic member and wire for elastic member

ABSTRACT

An elastic member is an elastic member formed of a wire having a cross section that is substantially circular, the cross section being orthogonal to a longitudinal direction, and the elastic member being expandable and contractible in a predetermined direction; and including: a first alloy portion that is made of an aluminum alloy having a tensile strength larger than 950 MPa and equal to or less than 1100 MPa at room temperature; and a second alloy portion configured to cover the first alloy portion, the second alloy portion having a thickness in a radial direction smaller than a radius of the first alloy portion, and being made of an aluminum alloy having a tensile strength of 100 MPa to 650 MPa at room temperature.

This Application is a Continuation of U.S. patent application Ser. No.15/740,634 filed on Dec. 28, 2017, which is National Stage Entry of PCTApplication No. PCT/JP2016/069142, filed on Jun. 28, 2016, which claimspriority from Japanese Application No. 2015-130303, filed on Jun. 29,2015. The entire contents of these applications are incorporated hereinby reference in their entirety.

FIELD

The present invention relates to an elastic member for an automobile,and a wire for the elastic member, the wire being used in manufacture ofthe elastic member.

BACKGROUND

Conventionally, as a method of realizing improvement of fuel efficiencyof automobiles, weight reduction of various parts thereof has beenpursued. For example, aluminum alloys have started to be used instead ofcast iron as a material for engine blocks, and magnesium alloys havestarted to be used instead of steel as a material for engine covers andoil pans.

In recent years, in terms of weight reduction of automobiles, use of amaterial made of an aluminum alloy in an elastic member of, for example,a suspension or the like, has been considered. As such aluminum alloys,6000 series aluminum alloys have been disclosed (see, for example,Patent Literature 1).

As aluminum alloys higher in strength than the above mentioned 6000series aluminum alloys, 7000 series aluminum alloys have been known. Ifa 7000 series aluminum alloy is used, an elastic member higher instrength than a bolt made of a 6000 series aluminum alloy is able to bemade.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 5335056

SUMMARY Technical Problem

However, 7000 series aluminum alloys are generally lower in stresscorrosion cracking resistance than 6000 series aluminum alloys, and thuswhen a 7000 series aluminum alloy is used in an elastic member, itsstress corrosion cracking resistance needs to be improved. Under suchcircumstances, an elastic member made of a material having improvedstrength and stress corrosion cracking resistance has been demanded.

The present invention has been made in view of the above, and an objectthereof is to provide an elastic member having improved strength andstress corrosion cracking resistance, and a wire for the elastic member,the wire being used in manufacture of the elastic member. Solution toProblem

To solve the above-described problem and achieve the object, an elasticmember according to the present invention is formed of a wire having asubstantially circular cross section orthogonal to a longitudinaldirection, expandable and contractible in a predetermined direction andincludes: a first alloy portion made of an aluminum alloy having atensile strength larger than 950 MPa and equal to or less than 1100 MPaat room temperature; and a second alloy portion configured to cover thefirst alloy portion, the second alloy portion having a thickness in aradial direction smaller than a radius of the first alloy portion, andbeing made of an aluminum alloy having a tensile strength of 100 MPa to650 MPa at room temperature.

Moreover, in the elastic member according to the present invention, thesecond alloy portion is formed of aluminum alloys being layered over oneanother, the aluminum alloys having different compositions from oneanother.

Moreover, in the elastic member according to the present invention, aradially outermost layer of the second alloy portion is smallest intensile strength.

Moreover, in the elastic member according to the present invention, aradially outermost layer of the second alloy portion is smallest inthickness.

Moreover, in the elastic member according to the present invention, aratio of the thickness of the second alloy portion to the radius of thefirst alloy portion is 0.01 to 0.2.

Moreover, a wire for an elastic member according to the presentinvention is a wire having a cross section that is substantiallycircular, the cross section being orthogonal to a longitudinaldirection, and includes: a core portion made of an aluminum alloy havinga tensile strength larger than 950 MPa and equal to or less than 1100MPa at room temperature; and an outer peripheral portion configured tocover the core portion, the outer peripheral portion having a thicknessin a radial direction smaller than a radius of the core portion, andbeing made of an aluminum alloy having a tensile strength of 100 MPa to650 MPa at room temperature.

Moreover, in the above-described wire for the elastic member accordingto the present invention, a ratio of the thickness of the outerperipheral portion to the radius of the core portion is 0.01 to 0.2.

Advantageous Effects of Invention

The present invention provides an effect that an elastic member havingimproved strength and stress corrosion cracking resistance, and a wirefor the elastic member, the wire being used in manufacture of theelastic member, are able to be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically illustrating a configurationof a suspension according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically illustrating a configurationof main parts of the suspension according to the embodiment of thepresent invention.

FIG. 3 is a sectional view along a line A-A illustrated in FIG. 2.

FIG. 4 is a perspective view illustrating a configuration of a wire forthe elastic member according to the embodiment of the present invention.

FIG. 5 is a sectional view schematically illustrating a configuration ofmain parts of a suspension according to a modified example of theembodiment of the present invention.

FIG. 6 is a perspective view schematically illustrating an example of apart, in which the wire for the elastic member according to theembodiment of the present invention is used.

FIG. 7 is a perspective view schematically illustrating an example of apart, in which the wire for the elastic member according to theembodiment of the present invention is used.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the appended drawings, a mode forcarrying out the present invention (hereinafter, referred to as“embodiment”) will be described. The drawings are schematic, a relationbetween a thickness and a width of each portion and ratios amongthicknesses of respective portions may be different from the actualrelation and ratios, and the drawings may also include a portion thatdiffers in relations or ratios among its dimensions mutually among thedrawings.

(Embodiment)

FIG. 1 is a perspective view schematically illustrating a configurationof a suspension according to an embodiment of the present invention. Asuspension 1 illustrated in FIG. 1 includes: an arm portion 2 that formsa framework of the suspension 1, and rotatably supports two disc rotors10, to which tires 101 are attached; coil springs 3 (elastic members)that are expandable and contractible in a direction substantiallyperpendicular to a direction in which the two disc rotors 10 face eachother; and shock absorbers 4 that attenuate force (vibration) exerted onexpansion and contraction operation of the coil springs 3. The discrotors 10 are each provided with a caliper 11 that is able to deceleraterotation speed of the disc rotor 10 by applying load to the disc rotor10 in a direction orthogonal to a rotation direction of the disc rotor10, with the disc rotor 10 inserted in the caliper 11. The suspension 1is installed in a vehicle body 100, and absorbs vibration transmittedfrom the tires 101 according to irregularities on road surfaces.

FIG. 2 is a perspective view schematically illustrating a configurationof main parts of the suspension according to the embodiment of thepresent invention, and is a perspective view illustrating aconfiguration of the coil spring 3. The coil spring 3 illustrated inFIG. 2 is made of a clad material formed by joining of two types ofaluminum (Al) alloys different from each other. The coil spring 3 ismade by a wire being spirally wound around, the wire being made of theabove mentioned clad material and having a cross section that issubstantially circular, the cross section being cut along a planeorthogonal to a longitudinal direction thereof. The coil spring 3 isexpandable and contractible in a predetermined direction (for example, adirection in which the coil spring 3 is stretched by being woundaround). In this specification, an aluminum alloy refers to an alloyhaving aluminum as a main component thereof.

The coil spring 3 has a first alloy portion 31 and a second alloyportion 32 that are respectively formed by use of two types of aluminumalloys different from each other. The first alloy portion 31 forms aportion at a radially inner side of the coil spring 3, and serves as acore portion of the coil spring 3. The second alloy portion 32 forms aportion at a radially outer side of the coil spring 3. That is, thesecond alloy portion 32 forms a surface layer portion of the coil spring3.

The first alloy portion 31 is made of an aluminum alloy containing: morethan 10.0 wt % and equal to or less than 17.0 wt % of zinc (Zn); andmore than 2.0 wt % and equal to or less than 6.0 wt % of magnesium (Mg),with the remainder containing Al and unavoidable impurities. The firstalloy portion 31 more preferably contains at least one or more typesselected from a group consisting of: 0.1 wt % or more and 3.0 wt % orless of copper (Cu); 0.05 wt % or more and 0.4 wt % or less of zirconium(Zr); 0.1 wt % or more and 2.0 wt % or less of manganese (Mn); 0.05 wt %or more and 0.5 wt % or less of iron (Fe); 0.1 wt % or more and 0.6 wt %or less of chromium (Cr); 0.05 wt % or more and 0.4 wt % or less ofsilicon (Si); 0.01 wt % or more and 0.1 wt % or less of vanadium (V);0.01 wt % or more and 0.2 wt % or less of titanium (Ti); 0.1 wt % ormore and 2.0 wt % or less of nickel (Ni); and 0.01 wt % or more and 0.6wt % or less of silver (Ag). The first alloy portion 31 has a tensilestrength larger than 950 MPa and equal to or less than 1100 MPa, at roomtemperature. A tensile strength has a value (for example in MPa)indicating a strength of a material. “Room temperature” referred toherein means temperature that is in a range of, for example, 15° C. to25° C., and that is constant at the time of measurement. The abovementioned tensile strength is obtained because concentrations of Zn andMg are high, and, in this case, because of occurrence of precipitationhardening due to a precipitate mainly composed of Zn and Mg.

Of the metals composing the first alloy portion 31, Zn provides aproperty of making the tensile strength high, and improving extrusionfor when a later described wire for the elastic member (a wire 300 forthe elastic member) is manufactured by an extrusion method. Mg providesa property of making the tensile strength high. Cu provides a propertyof making the tensile strength high, and improving stress corrosioncracking resistance. Zr provides a property of improving toughness, heatresistance, and the stress corrosion cracking resistance. Mn provides aproperty of making the tensile strength high, and improving thetoughness, the heat resistance, and the stress corrosion crackingresistance. Further, Fe provides a property of improving the heatresistance. Cr provides a property of improving the toughness, the heatresistance, and the stress corrosion cracking resistance. Ti and Niprovide a property of improving the heat resistance. Ag provides aproperty of making the tensile strength high, and improving the stresscorrosion cracking resistance.

The second alloy portion 32 is made of an aluminum alloy containing0.005 wt % or more and 6.5 wt % Zn or less of Zn, with the remaindercontaining Al and unavoidable impurities. The second alloy portion 32has a tensile strength equal to or larger than 100 MPa and equal to orless than 650 MPa, preferably equal to or larger than 350 MPa and equalto or less than 650 MPa, at room temperature. A radius of an outercircumference of the second alloy portion 32, that is, a radius of thewire of the coil spring 3 for the suspension 1 is, for example, equal toor larger than 8 mm and equal to or less than 15 mm.

The second alloy portion 32 preferably contains at least one or moretypes selected from a group consisting of: 0.05 wt % or more and 2.0 wt% or less of Mg; 0.1 wt % or more and 1.1 wt % or less of Cu; 0.01 wt %or more and 0.25 wt % or less of Zr; 0.051 wt % or more and 1.0 wt % orless of Mn; 0.05 wt % or more and 0.5 wt % or less of Fe; 0.05 wt % ormore and 0.3 wt % or less of Cr; 0.05 wt % or more and 1.3 wt % or lessof Si; 0.01 wt % or more and 0.1 wt % or less of V; 0.01 wt % or moreand 0.2 wt % or less of Ti; 0.1 wt % or more and 2.0 wt % or less of Ni;and 0.01 wt % or more and 0.6 wt % or less of Ag. Examples of analuminum alloy having such a composition include 6000 series aluminumalloys, for example, A6056. A6056 is an alloy having Al—Mg—Si as mainelements, and is known as an aluminum alloy having a comparatively hightensile strength and having improved stress corrosion crackingresistance.

A coating may be additionally formed around the second alloy portion 32.The coating in this case is formed by use of a material made of, forexample, anodized aluminum, and forms a layer having a thickness ofabout 1/100 of the radius of the outer circumference of the second alloyportion 32. For example, if the dimeter of the outer circumference ofthe second alloy portion 32 is 10 mm, the thickness of this coating isabout 0.1 mm. By the formation of this coating, antirust effect is ableto be improved.

FIG. 3 is a sectional view along a line A-A illustrated in FIG. 2. Across section illustrated in FIG. 3 is a cross section cut along theplane orthogonal to the longitudinal direction of the wire. Asillustrated in FIG. 3, when a radius of the first alloy portion 31 isd₁, and a thickness of the second alloy portion 32 in a radial directionthereof is d₂; a relation, “d₂<d₁”, is satisfied. More preferably, theradius of the coil spring 3, that is, the radius (d₁+d₂) of the outercircumference of the second alloy portion 32, and the thickness d₂satisfy a relation, “0.01≤d₂/(d₁+d₂)≤0.2”. Even more preferably, theradius (d₁+d₂) of the outer circumference of the second alloy portion 32and the thickness d₂ satisfy a relation, “0.05≤d₂/(d₁+d₂)≤0.15”.

FIG. 4 is a perspective view illustrating a configuration of a wire forthe elastic member, the wire being a wire for manufacture of the coilspring 3. The wire 300 for the elastic member illustrated in this figure(hereinafter, simply referred to as “wire 300”) forms a columnar shapehaving a two-layer structure including: a core portion 301 that is madeof the same aluminum alloy as the first alloy portion 31 and that iscolumnar; and an outer peripheral portion 302 that covers around thecore portion 301 and that is made of the same aluminum alloy as thesecond alloy portion 32. The wire 300 is manufactured by, for example,an extrusion method. Similarly to the above described first alloyportion 31 and second alloy portion 32, a ratio of a thickness of theouter peripheral portion 302 to a radius of the core portion 301, in thewire 300, is equal to or larger than 0.01 and equal to or less than 0.2.By this wire 300 being wound around, the above described coil spring 3is able to be manufactured.

According to the above described embodiment of the present invention, byformation of the two layer structure including: the first alloy portion31 that is made of the high strength aluminum alloy serving as the coreportion providing springiness of the coil spring 3 and that has thetensile strength larger than 950 MPa and equal to or less than 1100 MPaat room temperature; and the second alloy portion 32 that forms theouter surface, that is made of the aluminum alloy having improved stresscorrosion cracking resistance, and that has the tensile strength equalto or larger than 100 MPa and equal to or less than 650 MPa at roomtemperature; an elastic member having improved strength and stresscorrosion cracking resistance is able to be provided.

Further, according to this embodiment, since the radius (d₁+d₂) of theouter circumference of the second alloy portion 32 and the thickness d₂satisfy the relation, “0.01≤d₂/(d₁+d₂)≤0.2”, strength of the coil spring3 is able to be improved, while both this strength and improved stresscorrosion cracking resistance are able to be achieved.

Further, according to this embodiment, by formation of the wire 300 forthe elastic member, the wire 300 being the clad material including: thecore portion 301 that serves as the core portion providing thespringiness of the coil spring 3 and that is made of the high strengthaluminum alloy; and the outer peripheral portion 302 that forms theouter surface and that is made of the aluminum alloy having improvedstress corrosion cracking resistance; an elastic member (coil spring 3)having improved strength and stress corrosion cracking resistance isable to be formed by a manufacturing method similar to a conventionalmanufacturing method.

Further, according to this embodiment, since the radius (d₁+d₂) of theouter circumference of the outer peripheral portion 302 and thethickness (d₂) of the outer peripheral portion 302 satisfy the relation,“0.01≤d₂/(d₁+d₂)≤0.2”, strength and stress corrosion cracking resistanceof the elastic member that has been formed are able to be achieved withappropriate balance therebetween.

(Modified Example of Embodiment)

FIG. 5 is a sectional view schematically illustrating a configuration ofmain parts of a suspension according to a modified example of theembodiment of the present invention. FIG. 5 is a sectional view of acoil spring 3 a according to this modified example, and is a sectionalview corresponding to the line A-A in FIG. 2. In the above describedembodiment, an alloy portion (second alloy portion 32) made of analuminum alloy having improved stress corrosion cracking resistance hasbeen described as being provided in one layer on an outer peripheralside of the first alloy portion 31, but the second alloy portion may beformed of two or more layers. In this modified example, an example, inwhich a second alloy portion made of an aluminum alloy having improvedstress corrosion cracking resistance is in two layers, will bedescribed.

The coil spring 3 a illustrated in FIG. 5 is made of a clad materialformed by joining of three types of aluminum alloys different from oneanother. The coil spring 3 a is made by a wire being spirally woundaround, the wire being made of the above described clad material andhaving a cross section that is substantially circular, the cross sectionbeing cut along a plane orthogonal to a longitudinal direction thereof.The cross section may have a linearly symmetric shape, such as anelliptical shape, instead of the above described substantially circularshape.

The coil spring 3 a is formed of the first alloy portion 31 and a secondalloy portion 33 that are respectively formed by use of three types ofaluminum alloys having compositions different from one another. Thesecond alloy portion 33 has a first layer 33 a provided on the outerperipheral side of the first alloy portion 31, and a second layer 33 bthat is provided on an outer peripheral side of the first layer 33 a andthat forms a radially outer portion of the coil spring 3 a. That is, thesecond layer 33 b forms a surface layer portion of the coil spring 3 a.

The first layer 33 a and the second layer 33 b are aluminum alloys that:are formed by combination of types of metals that are the same as thoseof the metals used in the above described second alloy portion 32, inthe same composition range; have tensile strengths in the same range asthe second alloy portion 32; and have compositions different from eachother. Further, the first layer 33 a is equivalent to or larger than thesecond layer 33 b in tensile strength. That is, in a case where thetensile strengths of the first layer 33 a and the second layer 33 b aredifferent from each other, tensile strength of the coil spring 3 adecreases in order from the first alloy portion 31, to the first layer33 a, and then to the second layer 33 b.

As illustrated in FIG. 5, when a radius of the first alloy portion 31 isd₁, a thickness of the first layer 33 a of the second alloy portion 33in a radial direction thereof is d₃, and a thickness of the second layer33 b thereof in the radial direction is d₄; a relation, “d₄≤d₃<d₁”, issatisfied. More preferably, a radius of the coil spring 3 a, that is, aradius (d₁+d₃+d₄) of an outer circumference of the second alloy portion33, and a thickness (d₃+d₄) of the second alloy portion 33 satisfy arelation, “0.01≤(d₃+d₄)/(d₁+d₃+d₄)≤0.2”. Even more preferably, theradius (d₁+d₃+d₄) of the outer circumference of the second alloy portion33 and the thickness (d₃+d₄) satisfy a relation,“0.05≤(d₃+d₄)/(d₁+d₃+d₄)≤0.15”.

According to this modified example, by adopting a three-layer structureincluding: the first alloy portion 31 that serves as the core portionproviding the springiness of the coil spring 3 a and that is made of ahigh strength aluminum alloy; and the second alloy portion 33 that hasthe two-layer structure made of aluminum alloys having improved stresscorrosion cracking resistance; an elastic member having improvedstrength and stress corrosion cracking resistance is able to beprovided.

Further, according to this modified example, since the radius (d₁+d₃+d₄)of the outer circumference of the second alloy portion 33 and thethickness (d₃+d₄) of the second alloy portion 33 satisfy the relation,“0.01≤(d₃+d₄)/(d₁+d₃+d₄)≤0.2”, strength of the coil spring 3 a is ableto be improved, while both this strength and improved stress corrosioncracking resistance are able to be achieved.

In this modified example, in a case where the second alloy portion hasthree layers or more, a layer outermost in the radial direction has thesmallest thickness, and the smallest tensile strength.

Thus far, modes for carrying out the present invention have beendescribed, but the present invention is not to be limited only to theabove described embodiment. For example, the elastic member according tothe present invention maybe realized as another automobile part.

FIG. 6 is a perspective view schematically illustrating an example of apart, in which the wire for the elastic member according to theembodiment of the present invention is used. In the embodiment, the coilspring 3 for a suspension has been described as an example, but forexample, a stabilizer 5 illustrated in FIG. 6 may be an example. Thestabilizer 5 is able to be manufactured by the above described wire 300being bent. The stabilizer 5 is bent while expanding and contractingaccording to load applied thereon (direction in which the load isapplied). A radius of the outer circumference of the second alloyportion 32 in the stabilizer 5, that is, a dimeter of a wire of thestabilizer 5 is, for example, equal to or larger than 20 mm and equal toor less than 30 mm.

FIG. 7 is a perspective view schematically illustrating an example of apart, in which the wire for the elastic member according to theembodiment of the present invention is used. FIG. 7 is an example of astructure of a suspension of a vehicle. A torsion bar 61 is torsionallydeformed by receiving rotating force of a trailing link 6 of asuspension la illustrated in FIG. 7. Quality of a material of thistorsion bar 61 may be realized by use of the above described wire forthe elastic member. In addition, a door impact beam for an automobilemay be manufactured by the wire 300 being bent.

Further, in the present invention, a layer made of an aluminum alloyhaving improved stress corrosion cracking resistance may be additionallyprovided on a surface of the second alloy portion 32 or 33. For example,a 2000 series, 3000 series, 4000 series, or 5000 series aluminum alloyis an example of such an aluminum alloy.

Accordingly, the present invention may include various embodiments andthe like not described herein, and various design changes and the likewithin the scope of the technical ideas specified by the scope of theclaims may be made.

INDUSTRIAL APPLICABILITY

As described above, an elastic member, and a wire for the elasticmember, the wire being used in manufacture of the elastic member,according to the present invention, are useful in formation of anelastic member having improved strength and stress corrosion crackingresistance.

Reference Signs List

1 SUSPENSION

2 ARM PORTION

3, 3 a COIL SPRING

4 SHOCK ABSORBER

5 STABILIZER

10 DISC ROTOR

11 CALIPER

31 FIRST ALLOY PORTION

32, 33 SECOND ALLOY PORTION

33 a FIRST LAYER

33 b SECOND LAYER

100 VEHICLE BODY

101 TIRE

30

1-7. (canceled)
 8. An elastic member formed of a wire having asubstantially circular cross section orthogonal to a longitudinaldirection, the elastic member being expandable and contractible in apredetermined direction and comprising: a first alloy portion made of analuminum alloy having a tensile strength larger than 950 MPa and equalto or less than 1100 MPa at room temperature; and a second alloy portionconfigured to cover the first alloy portion, the second alloy portionhaving a thickness in a radial direction smaller than a radius of thefirst alloy portion, and being made of an aluminum alloy having atensile strength of 100 MPa to 650 MPa at room temperature, wherein thefirst alloy portion is made of an aluminum alloy containing: more than10.0 wt % and equal to or less than 17.0 wt % of zinc; and more than 2.0wt % and equal to or less than 6.0 wt % of magnesium, with the remaindercontaining aluminum and unavoidable impurities.
 9. The elastic memberaccording to claim 8, wherein the first alloy portion contains at leastone or more types selected from a group consisting of: 0.1 wt % or moreand 3.0 wt % or less of copper; 0.05 wt % or more and 0.4 wt % or lessof zirconium; 0.1 wt % or more and 2.0 wt % or less of manganese; 0.05wt % or more and 0.5 wt % or less of iron; 0.1 wt % or more and 0.6 wt %or less of chromium; 0.05 wt % or more and 0.4 wt % or less of silicon;0.01 wt % or more and 0.1 wt % or less of vanadium; 0.01 wt % or moreand 0.2 wt % or less of titanium; 0.1 wt % or more and 2.0 wt % or lessof nickel; and 0.01 wt % or more and 0.6 wt % or less of silver.
 10. Theelastic member according to claim 8, wherein the second alloy portion ismade of an aluminum alloy containing 0.005 wt % or more and 6.5 wt % Znor less of zinc, with the remainder containing aluminum and unavoidableimpurities.
 11. The elastic member according to claim 9, wherein thesecond alloy portion is made of an aluminum alloy containing 0.005 wt %or more and 6.5 wt % or less of zinc, with the remainder containingaluminum and unavoidable impurities.
 12. The elastic member according toclaim 10, wherein the second alloy portion contains at least one or moretypes selected from a group consisting of: 0.05 wt % or more and 2.0 wt% or less of magnesium; 0.1 wt % or more and 1.1 wt % or less of copper;0.01 wt % or more and 0.25 wt % or less of zirconium; 0.051 wt % or moreand 1.0 wt % or less of manganese; 0.05 wt % or more and 0.5 wt % orless of iron; 0.05 wt % or more and 0.3 wt % or less of chromium; 0.05wt % or more and 1.3 wt % or less of silicon; 0.01 wt % or more and 0.1wt % or less of vanadium; 0.01 wt % or more and 0.2 wt % or less oftitanium; 0.1 wt % or more and 2.0 wt % or less of nickel; and 0.01 wt %or more and 0.6 wt % or less of silver.
 13. The elastic member accordingto claim 11, wherein the second alloy portion contains at least one ormore types selected from a group consisting of: 0.05 wt % or more and2.0 wt % or less of magnesium; 0.1 wt % or more and 1.1 wt % or less ofcopper; 0.01 wt % or more and 0.25 wt % or less of zirconium; 0.051 wt %or more and 1.0 wt % or less of manganese; 0.05 wt % or more and 0.5 wt% or less of iron; 0.05 wt % or more and 0.3 wt % or less of chromium;0.05 wt % or more and 1.3 wt % or less of silicon; 0.01 wt % or more and0.1 wt % or less of vanadium; 0.01 wt % or more and 0.2 wt % or less oftitanium; 0.1 wt % or more and 2.0 wt % or less of nickel; and 0.01 wt %or more and 0.6 wt % or less of silver.
 14. The elastic member accordingto claim 8, wherein the second alloy portion is formed of aluminumalloys being layered over one another, the aluminum alloys havingdifferent compositions from one another.
 15. The elastic memberaccording to claim 14, wherein a radially outermost layer of the secondalloy portion is smallest in tensile strength.
 16. The elastic memberaccording to claim 14, wherein a radially outermost layer of the secondalloy portion is smallest in thickness.
 17. The elastic member accordingto claim 15, wherein a radially outermost layer of the second alloyportion is smallest in thickness.
 18. The elastic member according toclaim 8, wherein a ratio of the thickness of the second alloy portion tothe radius of the first alloy portion is 0.01 to 0.2.
 19. A wire for anelastic member, the wire having a cross section that is substantiallycircular, the cross section being orthogonal to a longitudinaldirection, the wire comprising: a core portion made of an aluminum alloyhaving a tensile strength larger than 950 MPa and equal to or less than1100 MPa at room temperature; and an outer peripheral portion configuredto cover the core portion, the outer peripheral portion having athickness in a radial direction smaller than a radius of the coreportion, and being made of an aluminum alloy having a tensile strengthof 100 MPa to 650 MPa at room temperature, wherein the core portion ismade of an aluminum alloy containing: more than 10.0 wt % and equal toor less than 17.0 wt % of zinc; and more than 2.0 wt % and equal to orless than 6.0 wt % of magnesium, with the remainder containing aluminumand unavoidable impurities.
 20. The wire for the elastic memberaccording to claim 19, wherein a ratio of the thickness of the outerperipheral portion to the radius of the core portion is 0.01 to 0.2.